You can verify this yourself by mixing some Epsom salt into water. Look at the solution. It shouldn't be cloudy.....

I'm thinking that something else is going on.... Could your fish be stressed out, and producing something that clouds the water more than usual?

Also, Epsom salt should not give a false negative for the ammonia, nitrate, or nitrite readings on your Test Kit. All three of these are nitrogen-containing compounds. But Epsom salt is MgSO4 (along with some water molecules attached). It also should not have a big effect on pH.

The tank water is not cloudy, but the vial when I test for ammonia is. It is not cloudy when I test for nitrites or nitrates; just ammonia. I was just unsure if the Epsom salt could affect the test results or not since it clouds the vial. I tested for ammonia, nitrites and nitrates and got 0, 0 and 10 ppm.

Thanks!

Edit: oh, it also affects the pH slightly, a differene of a little less than .2 (the ES treated tank is about 7.8 and the other tanks are 8). I don't think that it's a full difference of .2. It looks kind of in between 7.8 and 8.

Oh, sorry! I thought you were talking about the tank water. OK - I'm looking at the MSDS for the API Test Kit now....

Yes! It will make the ammonia test vial cloudy!

Ammonia Test Solution #2 contains sodium hydroxide. This reacts with the Epsom salt, forming some magnesium hydroxide. This has a low solubility in water, which would result in cloudiness.

Not sure about the false negative, but it's definitely a potential issue since the side reaction (formation of magnesium hydroxide) is occurring, which means there's less hydroxide available for the test itself.

You may want to try adding an extra drop of Ammonia Solution #2 to the vial to counter the side reaction. (Solution #1 is OK. It's only #2 that has the NaOH.)

Also, you may want to contact API to ask about this. They could probably tell you whether a false negative is possible. (And whether you need the extra drop of Solution #2, since using it up faster means you'd reduce the number of times you could test.)

Haven't looked at the solutions for the nitrate or nitrite tests yet, but it's 3am, and my brain is oatmeal. Will look at those tomorrow, if you'd like.